1. Field of the Technology
The present invention relates to a cutting tool which is optimally used for working, in particular, valve holes in a cylinder head of an engine.
2. Technical Background
Because a valve frequently comes into contact with an opening edge of such a valve hole of the cylinder head, a hard member made of, e.g., a sintered alloy is fitted at this part in order to improve durability or resistance to wear. A cutting tool which is used to work this valve hole includes a reamer such as a gun reamer for finishing a hole and a cutting tip for working the opening edge. The opening is frequently formed to have a tapered surface in conformity with the shape of a valve head. In order to form such a tapered surface, it is desirable that the cutting tip be mounted so as to be slidable a direction oblique to an axis of rotation of the cutting tool.
FIGS. 16 and 17 show an example of a prior art cutting tool used to work the above type of valve hole.
In FIGS. 16 and 17, a tool main body 1 has a substantially conic shape, and is mounted, e.g. at an end of a main shaft of an unillustrated machine tool via an adapter 2. The tool main body 1 is rotated about its longitudinal axis 0 so as to perform the cutting. A bushing 3 is mounted at the leading end of the tool main body 1 along the longitudinal axis 0. A shank of the aforementioned reamer (not shown) such as a gun reamer is fitted into the bushing 3. The hole can be finished by advancing the reamer while rotating the tool main body 1. The reamer is advanced by a shaft 4 coaxially inserted in a slide shaft to be described later.
Three cutting tips 5 are disposed on the outer surface of the leading end of the tool main body 1. The opening edge of the valve hole is worked by these cutting tips 5. It should be appreciated that only one cutting tip 5A is shown in FIG. 16, and the other two cutting tips 5B and 5C are not shown.
The two cutting tips 5B and 5C are directly secured on the tool main body 1, whereas the cutting tip 5A is slidably mounted on the tool main body 1. More specifically, the tool main body 1 is formed with a groove 6 having a T-shaped cross section as shown in FIG. 17 which extends along a generatrix of the conic shape of the tool main body 1, i.e. in a direction oblique to the longitudinal axis 0. A slider 7 is slidably fitted in the T-shaped groove 6, and the cutting tip 5A is detachably secured on the slider 7.
The tool main body 1 and the adapter 2 are formed with holes 1a and 2a, respectively, which extend along the longitudinal axis 0. A slide shaft 8 and a coupling member 9 are inserted into these holes 1a and 2a. The coupling member 9 is fitted in the hole 1a via a key 9a. Accordingly, the coupling member 9 is rotatable about the longitudinal axis 0 integrally with the tool main body 1, and is movable forward and backward in the hole 1a by moving the slide shaft 8 forward and backward. The T-shaped groove 6 of the tool main body 1 communicates with the hole 1a via a hole 6a opening in the bottom surface of the T-shaped groove 6. A coupling pin 10 which is projectable into the hole 1a via the hole 6a is mounted on the slider 7. The slider 7 and the coupling member 9 are connected by inserting the leading end of the coupling pin 10 into an oblique hole 9b formed in the coupling member 9. The slider 7 slides along the T-shaped groove 6 by moving the coupling member 9 forward and backward by means of the slide shaft 8. In other words, the cutting tip 5A slides in the direction oblique to the longitudinal axis 0.
The above-mentioned valve hole is worked by the thus constructed cutting tool as follows. First, the reamer such as the gun reamer is mounted on the bushing 3 and is pulled toward the base end of the tool main body 1 by means of the shaft 4. In this state, the tool main body 1 is rotated and moved forward along the longitudinal axis 0 to bevel the opening of the valve hole by the two cutting tips 5B and 5C. Subsequently, after the tool main body 1 is moved slightly backward, the slide shaft 8 and the coupling member 9 are moved forward while the tool main body is rotated so that the cutting tip 5A is slid via the coupling pin 10 and the slider 7 to form the aforementioned tapered surface at the opening edge of the valve hole. Thereafter, the reamer is moved forward by the shaft 4 while the tool main body 1 is kept rotating so as to finish the inner surface of the valve hole (valve guide hole).
While the tapered surface is formed at the opening edge of the valve hole by the cutting tool as described above, a cutting load acting on the cutting tip 5A is received by the wall surfaces (particularly, a wall surface facing in a rotating direction of the tool) of the T-shaped groove 6 of the tool main body 1 by way of the slider 7. Such a cutting load causes abrasion and deformation on the wall surfaces of the groove 6 after a long-term use. The wall surface are also abraded by a sliding movement of the slider 7 along the T-shaped groove 6.
The abrasion may cause the slider 7 to slide in a shaky manner, thereby reducing a working accuracy of the cutting tip 5A. Specifically, instead of making a linear sliding movement, the slider 7 makes a deviated movement at an abraded portion. As a result, the tapered surface does not form an accurate conic surface, but forms a curved surface bulging outward as in a drum.
In the case where such abrasion occurs in the above cutting tool, to re-adapt the device, the T-shaped groove 6 is widened and smoothed to form new wall surfaces, and a new slider 7 having dimensions and shape in conformity with those of the newly formed T-shaped groove 6 is remanufactured. In this way, the tool main body 1 is reused.
However, if the tool main body 1 is reused in the above manner, the T-shaped groove 6 and the slider 7 have to be reshaped and remanufactured, respectively, each time abrasion occurs. Accordingly, the operation inevitably becomes cumbersome. Especially, since the dimensions and the shape of the slider 7 change each time it is remanufactured, it has to be redesigned. Thus, the reuse of the tool main body 1 may lead to an uneconomical situation.
Further, if abrasion occurs, the T-shaped groove 6 and the slider 7 have to immediately be smoothed and replaced, respectively. Accordingly, a maintenance has to be relatively frequently performed.
Furthermore, since the cutting tip 5A is positioned by the engagement of the slider 7 and the T-shaped groove 6 in the above cutting tool, there is no room to correct shaping errors of the groove 6 and the slider 7. In order to obtain a desired working accuracy, the T-shaped groove 6 and the slider 7 have to be shaped with a high accuracy, thereby making the shaping difficult. There is also a limit in improving the mount rigidity of the slider 7. Insufficient mount rigidity may partially cause the slider 7 to exhibit a shaky movement.